Method of and apparatus for utilizing energy of a vibratory nature



5 Sheets-Sheet 1 0 F. M. BEST Filed May 51, 1950 Aug. 13, 1935.

METHOD OF AND APPARATUS FOR UTILIZING ENERGY OF A VIBRATORY NATURE [vi /7 /L INVENTOR Fran/2 M Bes/i ATTORNEY F. M. BEST 2,010,806

Aflg. 13, 1935.

METHOD OF AND APPARATUS FOR UTILIZING ENERGY OF A VIBRATORY NATURE 5 Sheets-Sheet 2 Filed May 31, 1930 INVENTOR Fran/i M Besi ATTORNEY Aug. 13, 1935. F. BEST 2,010,806

METHOD OF AND APPARATUS FOR UTILIZING ENERGY OF A VIBRATORY NATURE Filed May 31, 1930 5 Sheets-Sheet 5 INVENTOR Fro/7k M 563/ BY flYQ- ATTORNEY Aug. 13, M; BE

METHOD OF AND APPARATUS FOR UTILIZING ENERGY OF VIBRATORY NATURE Filed May 31, 1930 5 Sheets$heet 4 5 MW'IA'M mun-MM INVENTOR Fran/f M 565/.

ATTORNEY Aug. 13, 1935. F. M. BEST FOR UTILIZING ENERGY OF A VIBRATORY NATURE Filed May 31, 1930 5 Sheets-Sheet 5 METHOD OF AND APPARATUS INVENTOR T 51 Fro/M M 563% ATTORNEY Patented Aug. 13, 1935 UNITED STATES PATENT OFFl'ci METHOD OF AND APPARATUS FOR UTILIZ- ING ENERGY OF A VEBRATORY NATURE Application May 31, 1930, Serial No. 458,598 In Great Britain June 10, 1929 25 Claims. (Cl. 181-31) The present invention relates to methods of and apparatus for utilizing energy of a vibratory nature and translating such energy, either from air or a surrounding medium, into an electric circuit for electrical transmission, or from an electrical circuit into the air or surrounding medium for detection by the ear or by other means. The invention also relates to methods of making such apparatus.

The practical range of musical sounds is comprised between 40 and 40% vibrations per second. Below 40 vibrations the musical character of the tones is imperfect, as they are near the lower limit of audibiiity. Audible notes are, however, sometimes employed going as low as Cl with 16 vibrations, produced by a pipe about 32 feet long. A 65 foot pipe is present in some organs to produce a vibration of 13 5, cycles which is inaudible but which produces tone color when combined with higher notes. At the upper end of the scale of musical instruments, the piccolo flute has a fundamental of 4752 vibrations. This range of about eight octaves does not, however, cover the entire range of audibility, for the upper limit is very much above the musical scale, being from 30000 to 40000 vibrations per second, depending upon the individual.

Sound vibrations produced by musical instruments, the voice, or otherwise are exceedingly complex, being made up not only of the fundamental but also or" overtones and undertones which give the sound its quality and character. These may range from below the limit of audi bility to be at or near the upper limit.

Microphones are employed to collect sound waves and to convert the vibratory sound energy into electric currents of a wave form intended to correspond with the sound received. The microphones heretofore available, however, have not been capable oi responding to this wide range of frequency with the result that the lowest not s and the high overtones are lost and not transmitted. Some or" the qual t y and tone color of the original is inevitably blocked oil or absorbed, as it were, in the microphone Microphones, as employed in broadcasting studios, have the dis advantage of responding to echos and other modifications produced upon the sound by the walls of the room or by objects in the room, thus making it necessary to sound proof the studio, depriving the performers; of natural surroundings and the listeners of the not tone which would be available under ordinary conditions.

Loud speaking apparatus heretofore employed, whether for radio loud speakers or phonographs for the home, or for public addres systems, theatres, talking movies or elsewhere, has generally utilized a born for mechanically amplifying the sound reproduced by a comparatively small diaphragm under the influence of a single 5 armature actuated by voice coils, or have employed a paper or similar cone which is actuated by a single armature and acts as a tympani/en or diaphragm.

The horn type of speaker has been found more satisfactory for producing sounds of large volume for theatre work, but it lacks the property of natural reproduction of voice and music. The small diaphragm employed is incapable of forced vibration to reproduce the undertones and over tones which give quality to the voice and music.

It reproduces some tones in a volume which is out of proportion with that given other tones and the resulting distortion renders the reproduction artificial and unnatural. This defective reproduction is more apparent in installations of the horn type speaker requiring great penetration than where shorter penetration only is required because of the greater Work imposing on the diaphragm which cannot be increased in size correspondingly.

The cone type speaker has superseded the horn type speaker for small installations in radio receiving sets and phonographs for home use but has not been found satisfactory for theatre use for many reasons, principally because, when made of sufficient size and power, it does not remain in adjustment.

These types of loud speaking apparatus prpagate the sound in directions determined by the configuration of the apparatus. hey act, as it were, to pump the sound, and to obtain the necessary penetration for filling a large auditorium it is necessary to operate them to give tremendous volurne adjacent the unit of the speaker. 40

It has for a long time been known that the quality and tone value of stringed music instruments, such as the piano and violin, could be modified and greatly enhanced by using wood, not only for reinforcing the sound vibration sent out by the string or wire, but also for the purpose of modulating or retransmitting the sound received but with more tone color. The piano employs a sounding board made of selected Wood, and the quality of the music obtained from the piano depends to a large extent upon the sounding board to create the color of the music. The sounding board reacts not only to the fundamental sounds but also stimulates the overt-one and undertones. It creates low tones materially below the lowest note of the piano and overtones materially higher than the highest tone.

In the bass Viol, cello, viola and the violin, there is a material difference in the octave or ctaves that are covered. The difference is due to the size, length and thickness of the string; also the length and thickness of the particular grain in the edge-grain quarter-sawed spruce in each of the above named instruments. Characteristically, a violin is high in tone but, nevertheless, must have a certain proportion of bass. This is accomplished by a large G string plus a bass bar to thicken the wood on the front or belly of the violin sufiiciently to get proper vibration for base registry. This is also true of the viola, cello and base viol.

In the violin the quality of the music to be produced depends almost entirely upon the wooden parts ofthe violin. The ability of the trained ear to, recognize the maker of the instrument from its music is: almost entirely due to the character imparted to the music by the sounding hoard or analogous part. This character depends not only on the dimension of the parts but on the kind of wood used, its age and treatment.

The present invention contemplates the em ployment of a wooden sounding board or tympanum of a size at least large enough to be capable of naturally responding to all sound vibrations included in the range of audibil'ity, and preferably one capable of responding" to vibrations far. below and far above this range. A comparatively small board may have a range of 25 to 17000 vibrations, while a medium sized board may range from 6 to 69000 vibrations, and a large one from 2 to 71000 vibrations per second.

Such a board, when in a loud speaker, may pro duce all the sounds one can possibly receive, and when employed as a microphone may generate currents of corresponding range of frequencies.

diagonally. This provides an arrangement wherein there are short grains at two corners and a number of long grains near the diagonal.

The strips are secured to transverse vibration distributing members preferably made of spruce, the strips being glued to these vibration distributing members. By glueing these strips crosswise of the grain, one is able to get not only the fundamental note of music or voice, but also to get all color along with it, as although we may hit a fundamental note, the bar must be there and reach far enough to get its upper or lower harmonics or color frequencies, and also to act as a definite stop or barrier, preventing too many overlapping harmonics or color frequencies. This assemblage may then be secured to a heavy, rigid frame, preferably made of hard wood, such as maple.

At some stage of this process the diaphragm is submitted to a dressing operation, so that. one corner of the diaphragm, having the short grains of wood, is thinner than the opposite corner. of the Wood of the sounding board, so that equal This dressing operation cuts ofi part length grains on the opposite side of the diagonal are of unlike thickness and have different depth of tone.

Experiment has shown that a sounding board made up as just briefly described has a wide range of natural frequencies. The longer grain portion of the wood has very low frequency, while at the corner opposite the frequency is very high, it being higher on the thin side than on the thick side. A sounding board made in thi manner can be responsive at the corner to Very high vibrations, way beyond the limit of audibility of the human ear, and reproduce lower or baritone notes at or near the thick corner, and the longer diagonal can reproduce notes down to and below the limit of audibility. The susceptibility of such a diaphragm to send out such a range of notes may easily be shown by merely tapping the diaphragm at the various points. It may be measured by employing tuning forks and galvanometers.

I have discovered, however, that th simple Wood diaphragm may be too self-resonant, and that its acoustical properties may be improved and corrected by rendering pithy portions of the wood less sonorous, so that they act as a mute for the grain portion of the Wood which is the principal vibrating portion. It, therefore, becomes desirable to permanently soften the pithy portion of the wood, so thatit acts somewhat analogous to the mute on the violin or to the felts on the piano, whereby the vibration of the grain portion .of the wood cannot continue after the exciting source has disappeared.

A suitable material for acoustically correcting the wood is available in the form of rubber latex in a suitable solvent, such as benzine. Instead of rubber latex, one can use other analogous material, such as the latex from milk wort, or liquid cellulose. 7

As this sounding board has parts naturally responsive. to a wide range of frequencies, it has been found to be well fitted for reproducing voice and music in a most natural manner. The sounding board is of large extent, so that connected to vibratory electro-inagnetic sound reproducing apparatus in such a manner that the impulses produced in the apparatus are resolved into their component frequencies and transmitted to the board for reproduction only by the portions of the diaphragm capable of vibrating in accordance therewith. It has een found that a comparatively limited number of connections between the sounding board and the electro-magnetic reproducers are sufiicient for actuating the sounding board through its entire range of audible frequencies. The parts of the sou ding board which do not respond to the ireque the current employed in the coils appear to be substantially rigid and transmit the energy to the portion or portions of. the board which may respond.

Other and further objects of the invention will appear as the description proceeds.

The accompanying drawings illustrate several forms of sound reproducing apparatus together with the method of acoustically correcting the wood employed therein.

. In these drawings:

Figure l is a rear elevational view of a comparatively large unit adapted for use as a loud I speaker in an auditoritun, theatre or hotel lobby;

Figure 2 is an end view of the same with parts omitted;

Figure 3 is a diagonal sectional view on the ill line 3-3 of Figure 1 showing the arrangement of the wooden strips;

Figure 4 is a diagrammatic horizontal sectional view through an installation employing the sounding board with one form of sound reflector and with two sets of sound reflecting or modifying fins, this view being taken on the line 4-4 of Figure 5;

Figure 5 is a front elevational view of the ap paratus shown in Figure 4;

' Figure 6 is a vertical sectional view on the line 6-5 of Figure 5 showing the reflector provided with sound modifiers or reflecting fins analogous to the chiming post and base bars used in certain forms of stringed musical apparatus;

Figure 7 is a sectional view approximately on the line 'l-l' of Figure 1 illustrating an electric operating unit and its connections with the sounding board;

Figure 8 is a View in the direction of the arrow 8 of Figure 1 showing the units at right angles to the direction of Figure 7;

Figure 9 is a diagrammatic sectional view through a modified arrangement of sounding board and sound reflector where the sounding board is used for the moving picture screen;

Figure 10 is an enlarged side elevational view of the lower part of an electro-magnetic innit;

Figure 11 is a sectional view taken on the line H-H of Figure 10;

Figure 12 is a view partly in section showing the connection between the electromagnetic unit and the vibration distributing member;

Figure 13 is a. fragmentary wiring diagram;

Figures 14, 15, and 16 are diagrammatic illustrations showing the treatment of the wood for sound correction;

Figure 1'? is a rear elevational view and Figure 18 is a sectional view on the line i8l 8 of Figure 17, these figures showing a small form of sound reproducing unit utilizing two electro-magnetic units with vibration di tributors extending to the various vibration distributing strips;

Figures 19, 20, and 21 are front elevational, top plan and side elevational views of the frame work of a large form of reflector for a sound reproducer and showing means for supporting the sound diaphragm; and

Figure 22 is a diagrammatic illustration showing the method of sawing the log to produce the strips of wood used in the sounding board.

The sounding board may be made up of various sizes ranging from a size suitable for use as a loud speaker in ordinary home-size radio receiving sets, (such as 30" x 20") or it may be made to have very large dimensions (for example 36 x 20) where used in very large auditoriums. The size of the sounding board unit is gauged according to the size of the room in which it is desired to use it or the distance to which it is desired that the sound shall penetrate. The sounding board illustrated in Figure l is of a medium size, suitable for use in a moderate sized theatre or hotel lobby, while the sounding board illustrated in Figures 1'7 and 18 is of a small size, suitable for a radio receiving set or a phonograph for home use.

The vibratory diaphragm of the sounding board consists of a plurality of wooden strips 39, se cured to a rectangular wooden frame having top and bottom frame members 3| and side frame members 32. Various kinds of wood may be employed with varying sound properties. This frame is preferably made of heavy strips of hard maple, lap jointed and dowelled as indicated. The

rear faces of the boards 33 are secured to transverse vibration distributing members 33 which extend diagonally of the frame at right angles to the diagonal direction of the boards or strips 39.

It has been found that the best material to use in this sounding board consists of edge-grain quarter-sawed spruce for the vibrating dia phragm vibration distributing members, and hard maple for the frame. The quality is improved by using as hard grain wood as is available. This e gegrain quarter-sawed spruce is produced (see Figure 22) by quartering a spruce log A as indicated at aa. and then sawing the quartered log so that the grain will be on edge, as diagrammatically illustrated by the boards indicated to be cut in said Figure 22. These boards are then dried in a most careful manner, so as to prepare them for use without the development of cracks or checks. After careful selection, the dry boards are dressed to size and shape and glued together and to the vibration distributing members 33, also preferably made of strips of hard spruce with the grain running lengthwise. This will produce a diaphragm in which all the grains are parallel, as indicated by the long shading in the upper right hand corner of Figure l.

The vibration distributing cross members are secured to the sounding board strips very carefull and each grain in the sounding board strips (except possibly the extremely short ones at the corners) touches at least one of the vibration distributing members. The grains are, therefore, adapted to be actuated by one or more of the vibration distributing members in the manner above referred to.

The strips employed in the sounding board may have a thickness of approximately three-eighths of an inch before finishing. A rectangular sounding board made of wood strips of uniform thickness would be substantially symmetrical so far as sound qualities are concerned on opposite sides of the diagonal extending crosswise of the boards or strips. In order to avoid this duplication and to give the sounding board a much wider range of tone or natural frequency, the sounding board, when assembled on the transverse vibration distributing strips, is subjected to a dressing operation whereby the board is beveled, as it were, in the direction transverse of the grains of the strips. The board, which may be three-eighths of an inch thick, is passed through a planer in the direction of the grain and adjusted so as to trim on more from the short strip at one corner of the board than the short strip at the other corner of the board. For practical purposes it has been found that a satisfactory variation in thickness may be had by trimming the thick corner to a thickness of five-sixteenths of an inch and the thin corner to a thickness of three-sixteenths of an inch, the trimming being done uniformly across the width of the board. In this manner one can obtain a board wherein grains of equal length on opposite sides of the diagonal have dif ferent natural requencies or depth of tone.

In larger boards wherein the diagonal is of a length above 48 inches, it has been found that the natural frequency of the boards of the size just referred to may extend down as low as 6 vibrations per second. Where it is desired to have the small board reach into a lower range and improve the base notes, the diagonal part of the board is made thicker, either by planing it to provide a longitudinal rib of thick grains, or a strip of wood of the desired shape may be glued to it in somewhat the same manner as the base bar is secured in a violin. This thickened portion is indicated at 35 in Figure 18.

- The ends of the vibration distributing members are preferably thinned, as indicated at 355, somewhat as commonly practiced in making sounding boards for pianos. The sounding board'is then secured to the frame 3l32, preferably by being clamped between the frame members 3l22 and a front facing board 35. The ends of the strips and the holes or slots provided for them in the frame members 31-32 are carefully shaped so that the desiredcross strips may be securely locked in place.

Such a sounding board has a wide range of natural frequencies, but for the purposes for which the present invention is intended it has been found to be too resonant and noisy. In

order to cut down or reduce this self-resonance and improve the acoustic properties of the wood of the sounding board, the board is treated with a material capable of acoustically correcting it. Such a material may be a solution of rubber latex in benzine, or one may employ cellulose acetate, milk wort or other rubber-like materials, though not necessarily material chemically like rubber, provided they have the desired physical properties of deadening the sound in the pithy part of the wood without interfering with the 30 sounding of the grain portion. These materials are absorbed by the pithy portion of the wood, artifically aging it so that it acts as a mute for the grains which are the sonorous parts of the wood.

This process of acoustically correcting the wood is indicated in Figures 14, 15, and 16, wherein Figure 14 is an enlarged View showing the grain at 58 and the pithy portion at' il. Figure 15 shows, by the stippling 42, the partial penetration of the rubber-like fluid, and Figure 16, employing the same reference characters, shows, by the stippling, the complete penetration of this fluid. This solution may be applied by brushing it onto the surface of the sounding board and allowing to soak in. Three applications appear to be sufficient for complete penetration of wood of the thickness referred to. The material dries very quickly and retains its elasticity indefinitely.

It has been found that this acoustically correcting process may be employed quite generally in musical instruments employing wood. For example, the tone of a violin is greatly improved. It may also be employed as a sound deadening means in the walls or" an auditorium.

Sounding boards of the type above described may be actuated by electrical units responsive to voice currents. In Figure 1 a typical layout of such'electrical units is illustrated, the details of these units being shown in Figures '7, 8, 10, 11,

and 12.

At the rear of the frame 3l32, a number of heavy diagonal cross members 56 are mounted. The number of these cross members will depend upon the number of units employedand the way that they are spaced on the back of the board. They are preferably made of heavy maple so as to form a rigid firm support. The units are indicated at 5 l They may all be alike, if desired,

. and may be of the design shown in my co-pending application, Serial No. 284,020. These units can briefly be described as having a field 52 made either of cast or laminated iron and surrounded by an energizing coil 53. All these energizing field coils are connected to a source of direct current, such as 110 volt D. C. lighting mains, as

between them.

indicated in Figure 13. The poles 54 and 55 of the field magnet are grooved, as indicated at 56, and slidable pole pieces 5? are secured between the poles 54 or 55 and non-magnetic supports 58. These pole shoes or pieces 5? may be moved toward or away from one another, as will be obvious from Figure 11, to vary the distance They are clamped together by bolts indicated at 59 and 8G.

The slidable pole pieces bl are reduced, as indicated at El and 62, to accommodate voice coils 63. The adjacent faces of the pole pieces 5l5l are preferably bevelled as indicated in Figure 11 and are spaced very close to an armature 64. .The gap is preferably of the order of about four-thousandths of an inch, although the gap may be wider, up to say eight-thousandths of an inch.

This armature 6- 1 is made of soft iron and is carried on the end of a substantially rigid support 65 composed of bell metal, free as possible of sulphur. The most satisfactory formula appears to be 80% copper, 20% tin scavenged by titanium. About 1 ounce of titanium is used for each ten pounds of metal. Such a bell metal strip in the length employed, about one and onehalf inches, is substantially inflexible, and an attempt to bend it so much as .0005 will cause fracture.

The armature 65 is connected by a rigid wire or rod 66, preferably in the form of a phosphorbronze rod having a diameter of about No. 14 B and S gauge. This rod is connected with the sounding board. A convenient form of connection is to employ a four-jawed chuck. One part of this clutch, indicated at Bl, is threaded onto one of the wooden'cross pieces 23, as indicated in Figures '7 and 12. It is threaded tightly in place and the wire 85 passed into the open end. After the unit has been secured to the supporting frame member 56, the part 6? of the clutch is held against rotation and the part 68 threaded down to close the check against the wire 65. This forms a very secure connection between the armature E4 and the vibration distributing member 33 and does not disturb the position of the armature in the magnetic field.

In the illustrative example shown in Figure 1, fourteen of these units are employed, one being secured to each of the cross members 33, and three of these cross members having two of the units connected to them. The number of units to be employed on a given board will depend upon the size of the board and the number of octaves desired and the amount of vibratory energy which it is desired to transmit through the board. From twelve to eighteen units may be employed on boards of from, say, four to twentyfive square feet area, while for boards of much larger size, such as 9 X 16 feet, fifty-six units may be employed. For still larger boards more units would be employed.

The location of the units on a particular board would depend on thephysical characteristics of the board and the range of notes which it is desired to reproduce. Two, three or four of the units may be secured to a single vibration distributing member 33. The proper point at which the units are to be located is determinedeXp-erimentally by locating'various points in the board which have desired natural periods and then securing the unit at as near this point as possible. The units can be located within the distance of an inch or so from this point without materiallyaffecting the action of the board. In the very large boards it is possible to place the units so that they will function especially well for certain diilicult notes, such as those that are obtained from specific instruments ordinarily difficult to reproduce, such as French horns. Once the lon of the units has been determined for a particul r sized board, the same or substantially the same location or layout may be employed for other boards of the same size.

The units which have been described are wound to have an impedance of about 4000 ohms when the voice coils are in series parallel. Four of these units may be placed in parallel to give an impedance of about 1000 ohms which works against the output of an amplifier of about 50-1) ohms impedance. The manner in which the coils in the unit are connected together and the way the units are wired to the amplifier circuit may be varied to suit various conditions which may arise. The voice current may be passed through a number of amplifiers each feeding a selected set of units. The wattage employed per unit may range from 2 to 250 watts.

When this current is applied to the circuit of the voice coils, it presumably flows through all the coils. If the modulated current supplied to the units corresponds to a complex combination of a great many tones having varying pitches, the combination of sound reproducing units and the sounding board acts to analyze or resolve the said complex sound into a plurality of frequency bands, each band being reproduced to the greatest extent by the grains of corresponding frequency, thereby giving tone color to the reproduction. It, however, does not seem to actuate all the armatures, for such armatures as are connected to parts of the diaphragm having a natural frequency other than the frequency of the voice current are held stationary by the sub stantially rigid diaphragm and cross pieces.

In any proper layout of units, however, some armature in the set will be connected to a cross piece which in turn is connected with a grain of the desired natural frequency so that the grain will vibrate. The unit or units selected by the sounding board for vibration will function to actuate the sounding board and produce the sound of the fundamental and with all the overtones and undertones present in the wave form of the voice current passing through the coils. For example, if a very high note is to be produced, it will come from a shorter length of grain near one of the corners of the board, depending upon its particular frequency. This part of the board will vibrate while all the other parts ofthe board, except those having to do with particular overtonesand undertones of this fundamental, will remain quiet. It may be that only one of the units will appear to be functioning, the other being a parently dormant. When, however, a base or low note is to be produced, the sound will be obtained from the longer and thicker grains of wood in the sounding board, and a corresponding unit or units will work.

In this manner the sounding board is able to respond to the frequency of the current in the voice coils, and only such voice coils appear to function as are connected to the parts of the sounding board required for producing the note with its overtones and undertones present in the voice current. The fact that difierent parts of the diaphragm or sounding board vibrate when difierent frequencies or tones are produced can readily be demonstrated by merely touching dif- ,:ferent parts of the sounding boardv as the device operates. At one time one part of the board will be violently agitated and at another time, when another note is struck or reproduced, some other part will be agitated. When a full orchestra is being reproduced, the entire board seems to be vibrating.

As soon as the source of the impulse is removed, the acoustically corrected wood in the diaphragm immediately stops the Vlbl'zthe adjacent grains and stops these particular sound waves, so that there is no carrying over or blasting after it is desired that the particular be silenced.

It has been found that the sounding board type speaker which has been described will not function properly with loud speaker units of the type ordinarily used in cone and horn type speak crs. If a plurality of these units is employed, it appears that they all try to work at the same time and they burn out, whereas with the type of unit which has been described, the enormous power necessary may be continuously applied through these units. They remain entirely quiet until such time as the proper voice current frequency is received, so that the unit may actuate the desired part of the diaphragm.

In some cases, especially in smaller sized boards, it is desirable to reduce the number of electrical units employed, and in Figures 17 and 18 a small board having two units is illustrated. These units 5| may be the same as have been described, but instead of connecting its actuating wire 66 directly with the vibration distributing member 33,. the wire or rod 56 is connected to a spider having a number of arms 19. These arms are designed to have natural frequencies of vibration about an octave apart and are of diiierent lengths and thicknesses, connected with the vibration distributing members 33 somewhat as indicated. The entire spider is preferably made of the same type of metal as described for use in the member 65. When connected with the vibration distributing members, they are substantially rigid and transmit the vibratory energy to the sounding board to cause it to reproduce the desired music. One of these spiders may be employed with a small board or two of them with a slightly larger board.

Variations of this spider arrangement may be employed on larger boards, either to reduce the number of units employed or to augment the coloring in certain parts of the instrument. For example, a bridge may connect one unit to two of the ribs 33.

Sounding boards made up as above described propagate the sound in an entirely different manner from that present horn and cone type speakers. Whereas these speakers propagate the sound in the direction of the mouth of the horn or cone, the present apparatus propagates the sound in all directions. As the sounding board vibrates, it disturbs the air on both sides and starts a sound wave with a wide front which extends in all directions. When the speaker is working in a manner suflicient to fill a large auditorium with sound of the desired volume level, it does not, like other speakers, have an exceedingly great volume of sound adjacent the speaker. The present speaker can operate in a large auditorium at so low a volume level near the speaker as not to be deafening, whereas in horn and cone type speakers a deafening volume is necessary for obtaining a reasonable penetration of sound.

Another diiference in the manner in which the .present speaker propagates the sound becomes apparent when this type of speaker is compared with the conventional public address system. In

the public address system it is necessary to locate the horns a considerable distance from the speaker in order that the speaker can hear his own voice and modulate it accordingly, but with the present type of loud speaker, it may be close to the person delivering the address and yet this person hears his own voice and is able to modulate it accordingly without being deafened by the loud speaking apparatus.

For theatre work it is desirable to have as much of the sound as possible directed out toward the auditorium and, hence, the sounding board is'mounted in front of a reflector somewhat as indicated in Figures 4, 5, 9, 19 or 20. In the arrangement shown in Figures 4 and 5, the speaker unit 86 is placed behind a moving picture screen M in front of a reflector 82. This reflector may be spaced well back of the sounding board so as to permit one to get in behind the board for adjusting the units. The reflector 82 may be made of wood, concrete or'other suitable sound reflecting material. It functions somewhat the same as the reflector placed behind a band or orchestra. To bring out certain of the notes it has been found desirable to provide the reflector with sound deflecting fins, such as indicated at 83, 84' and 35. Thesesound deflecting fins may be oval shape, as shown in Figure 5. They are preferably made of acoustically corrected'spruce. The innermost set of deflecting fins acts analogous to the chiming post of a violin, whereas the outer fins act analogous to the base bar of a violin or similar instrument. They reinforce the sounds and appear to give them improved quality and tone. Two or more sets of these deflecting fins may be employed or a single set may be used. They may be located in various positions on the reflector,

depending upon various conditions which may arise. Where the reflector 82 is curved in a vertical direction, as shown in Figure 6, these sound deflecting fins are also preferably curved correspondingly. In the arrangement shown in Figure 9 the sounding board 813 is made large enough to act as thejmoving picture screen. The picture is framed on this sounding boardthe same as it would be framed onto an ordinary screen. The sounding board is provided with a suitable surface such as cold water paint to receive the picture. Here the reflector 82 is shown as being made of concrete and carries a single set of deflecting fins at Bl.

In Figures 19, 20, and 21 the frame work for a reflector is indicated. This frame work is made up of suitable bent steel bars 96 fastened to angle iron frame members 9!. The front frame members form a ring, as indicated in Figure 19, and at suitable points from this ring angle iron braces are extended in to support the sounding board indicated at 93.

While the foregoing discussion has related more particularly toward employment of the sounding boards and operating units for producing sound from electric currents of sound wave character, sometimes called voice currents, yet it has been found that this sounding board may be employed as a microphone for picking up sound and transmitting it electrically. The microphones employed in broadcasting studios require that they be placed in a sound proof room with attendant difficulties. Sounding boards such as have'been described are able to pick up the sound without being affected by surrounding objects and, hence, the present form of sounding board may be employed as a microphone by merely locating it in the wall of a studio or when placed near the speaker or orchestra. The currents generated in the coils may be combined and amplified or separately amplified and transmitted. It is not necessary to sound proof the room or remove ordinary objects.

It will be noted from the ranges of natural frequencies above given that these sounding boards are capable of natural vibration at frequencies both below and above the range of audibility. The upper register may be further increased by emplcying cedar instead of spruce in the thin corner of the diaphragm and, of course, the range may be varied by changing the thickness of the Wood. 7

The sounding board of the type described is also susceptible of use as a transmitter for wireless telephone and for cable code sending, wherein the different bands of natural frequency are employed in conjunction with electrical circuits for producing mechanical 'heterodyning.

What is claimed is:

1. The method of acoustically correcting a sonorous wooden structure which comprises applying a solution comprising an elastic, tenacious, non-crystalline material to fill the pithy portion of the wood and soften the same.

2. The method of acoustically correcting a, sonorous wooden structure which comprises applying a solution of rubber to the structure to fill the pithy portion of the wood.

3. The method of acoustically correcting a sonorous wooden diaphragm which comprises applying to the surface of the diaphragm a plurality of coatings of a solution comprising an elastic, tenacious, non-crystalline material until the pithy portion of the wood has been penetrated and softenedthereby.

4. The method of acoustically correcting a sonorous wooden diaphragm which comprises appithy portion of the wood has been penetrated thereby.

5. A treatment for wood to suppress the sonorous properties of the pithy portion thereof which consists in applying a solution of rubber to the wood to penetrate the pith of the wood.

6. The method of altering the sonorous properties of wood without interfering with the natural vibration of the grain portion of the wood which consists in applying an elastic, tenacious, non-crystalline material in solution to the wood to a sufficient extent to penetrate the pithy por-. tion thereof and soften the same.

7. The method of altering the sonorous properties of wood without interfering with the nat ural vibration of the grain portion of the wood which consists in applying a solution of rubber latex in a volatile organic solvent to a suflicient extent to penetrate the pithy portion thereof.

8. A wood board for acoustic purposes comprising a diaphragm made of wood the pithy portion of which is acoustically corrected by rubber absorbed therein.

9. A wood board for acoustic purposes comprising" a diaphragm made of soft wood the pithy portion of which is acoustically corrected by rubber absorbed therein.

10. A wood boardfor acoustic purposes comprising a diaphragm made of edge-grain quarter-sawed wood the pithy portion of which is acoustically corrected by rubber absorbed therein.

11. A wood board for acoustic purposes comprising a diaphragm of edge-grain quartersawed spruce the pithy portion of which acoustically corrected by rubber absorbed therein.

12. A wooden structure for acoustic purposes comprising a diaphragm made of a plurality of strips of edge-grain quarter-sawed wood arranged edge to edge the pithy portion of which is acoustically corrected by rubber absorbed therein.

13. A wooden str c for acoustic purposes comprising a diaphragm made of a plurality of strips of edge-grain quarter-sawed spruce arranged edge to edge and glued together and to cross members, the pithy portion of the diaphragm strips being acoustically corrected by rubber absorbed therein.

14. An acoustic diaphragm comprising a plurality of strips of wood mounted on a frame with the grain on edge and all the grain parallel, the frame being so shaped that the length of the grain portions varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other come, the thickness varying from one of said corners to the other, whereby the natural period of vibration of grains of equal length differs on opposite sides of the diagonal.

15. An acoustic diaphragm comprising a plurality of strips of wood mounted diagonally of a frame with the grain on edge and all the grain parallel, whereby the length of the grain portions varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corner, the thickness varying uniformly from one of said corners to the other, whereby the natural period of vibration of grains of equal length differs on opposite sides of the diagonal.

16. An acoustic diaphragm comprising a plurality of strips of wood mounted diagonally of a frame with the grain. on edge and all the grain parallel, whereby the length of the grain portions varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corner, the thickness varying from one of said corners to the other, whereby the natural period of vibration of grains of equal length differs on opposite sides of the diagonal, the thickness adjacent the diagonal being increased to lower the natural period of vibration and produce deeper tones.

17. An acoustic diaphragm comprising a plurality of strips of wood mounted on a frame with the grain on edge and all the grain parallel, the frame being so shaped that the length of the grain portions varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corner, the thickness varying from one of said corners to the other, whereby the natural period of vibration of grains of equal length differs on opposite sides of the diagonal, the pithy portion of the wood bearing absorbed rubber to acoustically correct it, whereby the pith acts as a mute for the grain.

18. An acoustic diaphragm comprising a plurality of strips or" edge-grain quarter s wed spruce mounted diagonally of a hard wood frame with the strips edge to edge, whereby the length of the grain portions varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corner, the thickness varying from one of said corners to the other, whereby the natural period of vibration of grains of equal length differs on opposite sides of the diagonal, and a plurality of vibration distributing members disposed transversely of the strips and glued to the same.

19. For use in a diaphragm of a sound reproducer, a wooden diaphragm of sufficient area to produce undesirable self-resonant effects, said diaphragm being impregnated with material adapted to dampen the vibration thereof, so as to substantially suppress said self-resonant effects.

20. The method of making a sound diaphragm which comprises, cutting a log to form quartersawed edge-grain lumber, drying said lumber, dressing to form boards, assembling a plurality of said boards edge to edge with the grain parallel and on edge to form a diaphragm, the diaphragm being so shaped that the length of the grain portion varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corner, securing the boards to transverse vibration distributing members and to a rigid outer frame, and surfacing the diaphragm in a direction transverse to the boards so that the short board at one corner is thinner than the short board at the other corner and has a natural frequency materially higher than that of the short board at the oth r corner.

21. The method of making a sound diaphragm which comprises, cutting a log to form quarter sawed edge-grain lumber, drying said lumber, dressing to form boards, assembling a plurality of said boards edge to edge v Lth the grain parallel and on edge to form a diaphragm, the diaphragm being so shaped that the length of the grain portion varies from a minimrnn at one corner to a maximum in the middle and then to a minimum at the other corner, securing the boards to transverse vibration distributing ZIlSn bers and to a rigid outer frame, surfacing the diaphragm in a direction transverse to the boards so that the short board at one corner is thinner than the short board at the other corner and has a natural frequency materially higher than that of the short board at the other corner, and applying a solution of sound suppressing material to suppress the noisy sonorous properties of the pithy portions of the wood.

22. The method of making a sound diaphragm which comprises, cutting a spruce log to form quarter-sawed edge-grain lumber, drying said lumber, dressing to form boards, assemblin a plurality of said boards edge to edge with the grain parallel and on edge to form a diaphragm, the diaphragm being so shaped that the length of the grain portion varies from a minimum at one corner to a maximum in the middle and then to a minimum at the other corn securing the boards to transverse vibration distributing mem bers of spruce and to a rigid outer frame of hard wood, surfacing the diaphragm in a direction transverse to the boards so that the short board at one corner is thinner than the short board at the corner and has a natural frequency materially higher than that of the short board at the other corner, and applying a solution or sound suppressing material to suppress the noisy sonorous properties of the pithy portions of the wood.

23. The method of making a rectangular sound diaphragm composed of wooden strips arranged substantially diagonally and glue together edge to edge, naturally responsive at th corners having short boards to notes of materially different pitch which consists in making one such corner thinner than the other.

24. The method of making a rectangular sound diaphragm composed of wooden strips out along the grain and arranged substantially diagonally and glued together edge to edge naturally rediaphragm composed of wooden strips out along the grain and arranged substantially diagonally and glued together edge to edge naturally responsive to a wide range of pitch which consists in dressing off the diaphragm to make it wedge shaped in a direction transverse of the grain of the wood.

' FRANK M. BEST. 

